asks those who believe in fairies to clap their hands? Well, I don't want you to believe in things you do not see, but when you see the Earth rotating, that is, when the shadow goes to the left instead of to the right, then you clap your hands; for then you will have seen the rotation of the Earth. Surely it is beginning to go over now, it is more to the left than to the right! (The audience here testified as requested.) In this way you can soon see the Earth rotating, if the experiment is carefully prepared beforehand.
There is another way in which it has been shown by M. Foucault that the Earth is rotating. He showed it by means of a gyrostat. He spun a top quickly and set it up in a certain position. Now a thing that is spinning has got a great tendency to remain in the same position. For instance, we know that a spinning top does not fall down, though it may turn round. I cannot show you M. Foucault's exact experiment, but I can show you some pretty things of the same kind which tell us as much as we want to know. Perhaps you have played with gyrostats already: but probably you have wound them up with string; Mr. Gray, of Glasgow, has invented some beautiful gyrostats which are wound up by means of a small motor. Here is one now spinning very quickly, and if I put it horizontally with one end of the axis on a stand, it will not fall down, as it would if it were not spinning, but simply goes round and round. Its weight tries to make it fall, but can only make it turn round. And if we try to lift the end of the axis, we only make it turn round the other way.
